U.S. patent number 11,442,002 [Application Number 16/901,352] was granted by the patent office on 2022-09-13 for cuvette having high optical transmissivity and method of forming.
This patent grant is currently assigned to California Institute of Technology. The grantee listed for this patent is California Institute of Technology. Invention is credited to Frank T. Hartley, Taeyoon Jeon, Amirhossein Nateghi, Axel Scherer.
United States Patent |
11,442,002 |
Scherer , et al. |
September 13, 2022 |
Cuvette having high optical transmissivity and method of
forming
Abstract
The present disclosure is directed toward optical elements, such
as sample cuvettes, lenses, prisms, and the like, whose
transmissivity is increased by the addition of a geometric
anti-reflection layer disposed on at least one surface of the
optical element, where the geometric anti-reflection layer includes
a plurality of geometric features that collectively reduce the
reflectivity of the interface between the surface and another
medium. As a result, more of an optical signal incident on the
surface passes through the interface. In some embodiments, every
surface through which an optical signal passes includes a geometric
anti-reflection layer. Due to the increased transmissivity of the
optical element, in some embodiments, the use of low-cost,
high-refractive-index materials, such as conventional silicon, is
enabled.
Inventors: |
Scherer; Axel (Barnard, VT),
Nateghi; Amirhossein (Pasadena, CA), Jeon; Taeyoon
(Pasadena, CA), Hartley; Frank T. (Arcadia, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
California Institute of Technology |
Pasadena |
CA |
US |
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Assignee: |
California Institute of
Technology (Pasadena, CA)
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Family
ID: |
1000006556266 |
Appl.
No.: |
16/901,352 |
Filed: |
June 15, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200309676 A1 |
Oct 1, 2020 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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16212347 |
Dec 6, 2018 |
10712258 |
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62595362 |
Dec 6, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N
21/35 (20130101); G01N 21/255 (20130101); G01N
21/171 (20130101); G01N 1/42 (20130101); G01N
1/44 (20130101); G01N 21/0303 (20130101); G01N
21/3577 (20130101); G01N 21/3504 (20130101) |
Current International
Class: |
G01N
21/03 (20060101); G01N 21/35 (20140101); G01N
1/42 (20060101); G01N 21/17 (20060101); G01N
21/25 (20060101); G01N 1/44 (20060101); G01N
21/3504 (20140101); G01N 21/3577 (20140101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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106323873 |
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Jan 2017 |
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CN |
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2545995 |
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Nov 1984 |
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FR |
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2777352 |
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Oct 1999 |
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FR |
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20120084090 |
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Jul 2012 |
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KR |
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2004/048929 |
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Jun 2004 |
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WO |
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2012/001370 |
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Jan 2012 |
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WO |
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WO-2014007401 |
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Jan 2014 |
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WO |
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2016/168386 |
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Oct 2016 |
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WO |
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Other References
Authorized Officer Blaine R. Copenheaver, International Search
Report and Written Opinion issued in International PCT Application
No. PCT/US2018/064340 and dated Jan. 31, 2019. cited by applicant
.
Authorized Officer Blaine R. Copenheaver, International Search
Report issued in International PCT Application No.
PCT/US2018/064340 and dated Jan. 31, 2019. cited by applicant .
Examiner initiated interview summary (PTOL-413B) dated Mar. 12,
2020 for U.S. Appl. No. 16/212,347. cited by applicant .
Examiner initiated interview summary received for U.S. Appl. No.
16/212,347, dated Mar. 12, 2020. cited by applicant .
Notice of Allowance and Fees Due (PTOL-85) dated Mar. 12, 2020 for
U.S. Appl. No. 16/212,347. cited by applicant .
Notice of Allowance and Fees Due (PTOL-85) dated May 1, 2020 for
U.S. Appl. No. 16/212,347. cited by applicant .
Notice of Allowance received for U.S. Appl. No. 16/212,347, dated
Mar. 12, 2020. cited by applicant .
Notice of Allowance received for U.S. Appl. No. 16/212,347, dated
May 1, 2020, 5 pages. cited by applicant .
Advisory Action (PTOL-303) dated Nov. 18, 2021 for U.S. Appl. No.
16/212,499. cited by applicant .
Examiner Interview Summary Record (PTOL-413) dated Nov. 18, 2021
for U.S. Appl. No. 16/212,499. cited by applicant .
Extended European Search Report issued in counterpart EP patent
application No. 18885676.9, dated Jul. 16, 2021, 7 pp. cited by
applicant .
Final Rejection dated Sep. 28, 2021 for U.S. Appl. No. 16/212,499.
cited by applicant .
Non-Final Office Action dated May 18, 2021 for U.S. Appl. No.
16/212,499. cited by applicant .
Requirement for Restriction/Election dated Mar. 11, 2021 for U.S.
Appl. No. 16/212,499. cited by applicant .
Non-Final Rejection dated Mar. 3, 2022 for U.S. Appl. No.
16/212,499. cited by applicant.
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Primary Examiner: Stafira; Michael P
Attorney, Agent or Firm: Kaplan Breyer Schwarz, LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This case is a continuation of co-pending U.S. patent application
Ser. No. 16/212,347, filed Dec. 6, 2018, which claims priority of
U.S. Provisional Patent Application Ser. No. 62/595,362, filed Dec.
6, 2017, each of which is incorporated herein by reference. If
there are any contradictions or inconsistencies in language between
this application and one or more of the cases that have been
incorporated by reference that might affect the interpretation of
the claims in this case, the claims in this case should be
interpreted to be consistent with the language in this case.
Claims
What is claimed is:
1. An optical element comprising a cuvette that includes: a body
that includes first and second surfaces, each of the first and
second surfaces comprising a first material; and a first plurality
of features that have substantially the same height, the first
plurality of features collectively defining a first geometric
anti-reflection (GAR) layer, each feature of the first plurality
thereof projecting outward from the first surface from a first base
located at the first surface to a first tip, wherein each feature
of the plurality thereof has a first cross-section that increases
monotonically from the first tip to the first base; a second
plurality of features that have substantially the same height, the
second plurality of features collectively defining a second GAR
layer, each feature of the second plurality thereof projecting
outward from the second surface from a second base located at the
second surface to a second tip, wherein each feature of the second
plurality thereof has a second cross-section that increases
monotonically from the second tip to the second base; wherein a
flat surface comprising the first material is characterized by a
first reflectivity for a first light signal; wherein the first GAR
layer and the first surface are collectively characterized by a
second reflectivity for the first light signal that is lower than
the first reflectivity; and wherein the second GAR layer and the
second surface are collectively characterized by a third
reflectivity for the first light signal that is lower than the
first reflectivity.
2. The optical element of claim 1 wherein the plurality of first
tips collectively defines a first boundary, and wherein the
refractive index of the first GAR layer increases adiabatically
from the first boundary to the first surface.
3. The optical element of claim 1 wherein the first cross-section
increases non-linearly from the first tip to the first base.
4. The optical element of claim 1 wherein the first material is
silicon.
5. The optical element of claim 1 wherein each feature of the first
plurality thereof comprises the first material.
6. The optical element of claim 1 wherein each feature of the first
plurality thereof has a sidewall that extends between the first
base and the first tip, and wherein at least one sidewall of the
first plurality thereof includes a surface feature.
7. The optical element of claim 1 wherein the first surface is
non-planar.
8. The optical element of claim 1 wherein the first light signal is
characterized by a spectral range that extends from a first
wavelength to a second wavelength, the first wavelength being
shorter than the second wavelength, and wherein the features of the
first plurality thereof are separated by an average spacing that is
less than the first wavelength.
9. The optical element of claim 8 wherein the first wavelength is 2
microns and the second wavelength is 15 microns.
10. An optical element that includes a cuvette for holding a test
sample, the cuvette comprising: a body that includes first, second,
third, and fourth surfaces, each comprising a first material that
is characterized by a first refractive index for a first light
signal; a first geometric anti-reflection (GAR) layer disposed on
the first surface, the GAR layer including a first plurality of
features that have substantially the same height and extend
normally from the first surface, wherein each feature of the first
plurality thereof extends between a first base located at the first
surface and a first tip located at a first boundary, and wherein
each feature of the first plurality thereof has a first
cross-section that increases monotonically from the first tip to
the first base, and further wherein the first boundary is
characterized by a first effective refractive index that is lower
than the first refractive index; and a second GAR layer comprising
a second plurality of features that extend normally from the second
surface, wherein each feature of the second plurality thereof
extends between a second base at the second surface and a second
tip, and wherein the plurality of second tips collectively defines
a second boundary that is characterized by a second effective
refractive index that is lower than the first refractive index.
11. The optical element of claim 10 wherein the optical element
comprises a lens or a prism.
12. The optical element of claim 10 wherein each feature of the
first plurality thereof comprises the first material.
13. The optical element of claim 10 wherein the first material is
silicon and the first light signal has a spectral width that
includes at least a portion of the mid-infrared spectral range.
14. The optical element of claim 10 wherein each feature of the
first plurality thereof has a sidewall that extends between the
first base and the first tip, and wherein at least one sidewall of
the first plurality thereof includes a surface feature.
15. The optical element of claim 10 wherein the first surface is
non-planar.
16. A method for forming a cuvette for holding a test sample, the
method comprising: providing a body having first, second, third,
and fourth surfaces that comprise a first material having a first
refractive index for a first light signal; forming a first
geometric anti-reflection (GAR) layer on the first surface, wherein
the first GAR layer includes a first plurality of features that
have substantially the same height and extend normally from the
first surface from a first base located at the first surface to a
first tip at a first boundary, and wherein each feature of the
first plurality thereof has a first cross-section that increases
monotonically from the first tip to the first base, and further
wherein the first boundary is characterized by a first effective
refractive index that is lower than the first refractive index; and
forming a second GAR layer on the second surface, wherein the
second GAR layer includes a second plurality of features that have
substantially the same height and extend normally from the second
surface from a second base located at the second surface to a
second tip at a second boundary, and wherein each feature of the
second plurality thereof has a second cross-section that increases
monotonically from the second tip to the second base, and further
wherein the second boundary is characterized by a second effective
refractive index that is lower than the first refractive index.
17. The method of claim 16 wherein the optical element is formed
such that it includes at least one of a lens and a prism.
18. The method of claim 16 wherein each of the first surface and
the first plurality of features is formed by etching a first
layer.
19. The method of claim 16 wherein the first plurality of features
is formed by depositing a second material on the first surface.
20. The method of claim 19 wherein the second material and the
first material are substantially the same material.
21. The method of claim 16 wherein the first GAR layer is formed
such that the first cross-section increases linearly from the first
tip to the first base.
22. The method of claim 16 wherein the first light signal is
characterized by a spectral range that extends from a first
wavelength to a second wavelength, the first wavelength being
shorter than the second wavelength, and wherein the features of the
first plurality thereof are separated by an average spacing that is
less than the first wavelength.
23. The method of claim 22 wherein the first wavelength is 2
microns and the second wavelength is 15 microns.
24. The method of claim 16 wherein each feature of the first
plurality thereof is formed such that it has a sidewall that
extends between the first base and the first tip, and wherein at
least one sidewall of the first plurality thereof includes a
surface feature.
Description
FIELD OF THE INVENTION
The present invention relates generally to optical analysis of a
test sample and, more particularly, to sample holders suitable for
use in optical analysis systems such as infrared spectrometers,
mid-infrared spectrometers, and the like.
BACKGROUND OF THE INVENTION
During optical analysis of a test sample, the sample is often held
in a sample chamber of a cuvette--particularly when the test sample
is a fluid or fluid-like substance. As a result, at least a portion
of the cuvette must be at least somewhat transparent for the
wavelengths included in the light signal used to interrogate the
sample (i.e., the interrogation signal).
For a variety of reasons, it is often desirable to use a
low-intensity interrogation signal. To enable an output signal with
high signal-to-noise ratio, therefore, materials used in prior-art
cuvettes are normally low-refractive-index materials, such as
glasses, plastics, calcium fluoride, and the like, which mitigates
the amount of optical energy lost in transiting the cuvette
itself.
Unfortunately, such materials can be inappropriate for use with
some test samples, due to interaction between the cuvette material
and the test sample, chemical incompatibility, etc. For more exotic
materials, such as calcium fluoride, material cost becomes a
significant disadvantage in some applications.
Furthermore, many optical analysis techniques are preferably
performed using interrogation signals having wavelengths for which
typical cuvette materials are not suitable. Mid-infrared
spectroscopy, for example, employs interrogation signals having
wavelengths within the range of 2 microns to 15 microns, over which
the transmissivity of common cuvette materials is poor.
The need for a cuvette comprising common, low-cost materials that
can be configured to have high transmissivity for the spectral
content of any of a wide range of interrogation signals remains, as
yet, unmet in the prior art.
SUMMARY OF THE INVENTION
The present disclosure is directed toward optical elements, such as
a cuvettes for holding test samples, lenses, prisms, or other
optical elements that interact with an optical signal, where the
reflectivity of at least one surface of the optical element is
reduced by the inclusion of a plurality of features at the surface,
where the features collectively define a geometric antireflection
layer. The features are configured such that the effective
refractive index of the geometric antireflection layer transitions
adiabatically from a relatively lower refractive index at its outer
boundary to a relatively higher refractive index where they meet
the surface on which they are disposed, where the higher refractive
index is typically the bulk refractive index of the material of the
surface. Embodiments of the present invention are particularly well
suited for use at wavelengths where optical elements require exotic
or expensive optical materials, such as the mid-infrared spectral
range.
Like optical elements known in the prior art, an optical element in
accordance with the present disclosure comprises a material that is
at least partially transmissive for the wavelengths included in an
optical signal such that at least a portion of the optical signal
can pass through at least a portion of the optical element.
Typically, however, the materials used in prior-art systems must
have low refractive indices to mitigate reflectivity at all
surfaces in the path of the optical signal. As a result, at
wavelength ranges such as the mid-infrared spectral range, only a
limited set of materials, such as glass, plastic, or exotic
materials (e.g., calcium fluoride, etc.) can typically be used. In
some prior-art optical elements, multi-layer dielectric coatings
are employed as anti-reflection layers at one or more of these
surfaces. Unfortunately, such multi-layer dielectric coatings
typically only reduce the reflectivity of its corresponding surface
over a very narrow wavelength range.
In sharp contrast to the prior art, optical elements in accordance
with the present invention have higher transmittance for an optical
signal by virtue of a geometric anti-reflection layer included at
one or more of its surfaces. The geometric anti-reflection layer
includes a plurality of features located at the surface, where the
spacing of the features is less than the wavelengths of light in
the optical signal, and where the features collectively suppress
reflections at an interface between the surface and a medium (e.g.,
air, a test sample, etc.) such that more light of the optical
signal can pass through the interface. A geometric anti-reflection
layer in accordance with the present disclosure can reduce the
reflectivity of the surface on which it is disposed over a
significantly wider spectral range than an anti-reflection coating
of the prior art. Furthermore, they can be coupled with surfaces
that comprise materials having higher refractive indices than are
typically desirable in prior-art optical elements. Therefore,
optical elements in accordance with the present disclosure provide
particular advantages when used in a system that operates in some
wavelength ranges, such as the mid-infrared spectral range.
An illustrative embodiment in accordance with the present
disclosure is a silicon-based cuvette suitable for use in
mid-infrared spectroscopy, where the cuvette has a sample chamber
that resides within its body. The body is formed by joining two
silicon substrates, one of which includes a cavity recessed from
one of its surfaces. At each surface of the cuvette through which
the mid-infrared interrogation signal passes, a geometric
anti-reflection layer is formed by etching into the bulk material
of the substrate back to define a plurality of features having a
cross-section that increases non-linearly from a relatively
small-diameter tip to a broad base at a second, new surface. The
features are spaced apart over the second surface by a distance
that is less than the shortest wavelength of light included in the
interrogation signal. The features are configured such that the
total aggregate surface area normal to the interrogation signal is
very small, thereby mitigating back-reflections of the signal.
In some embodiments, the features have a cross-section that
increases linearly from their tip to their base. In some
embodiments, the features are formed by disposing material on the
surface, for example, via selective-area growth, self-assembly, the
Langmuir-Blodgett method, atomic-layer deposition (ALD),
evaporation, sputtering, evaporative or sputtered deposition
through a shadow mask, and the like.
In some embodiments, the sidewalls of one or more of the features
are roughened by forming nanostructure in its surface via a
nano-structuring method such as electrochemical etching,
ion-assisted etching, etc.
In some embodiments, the body of the cuvette comprises two
substrates made of different materials.
In some embodiments, at least one surface of the cuvette through
which the interrogation signal passes does not include a geometric
anti-reflection layer.
An embodiment in accordance with the present disclosure is an
optical element comprising a body that includes a first wall having
a first surface comprising a first material; and a first plurality
of features that collectively define a first geometric
anti-reflection (GAR) layer, each feature projecting outward from
the first surface from a first base located at the first surface to
a first tip, wherein each feature of the plurality thereof has a
first cross-section that increases monotonically from the first tip
to the first base; wherein a flat surface comprising the first
material is characterized by a first reflectivity for a first light
signal; and wherein the first geometric anti-reflection layer and
the first surface are collectively characterized by a second
reflectivity for the first light signal that is lower than the
first reflectivity.
Another embodiment in accordance with the present disclosure is an
optical element comprising a body that includes a first wall having
a first surface that comprises a first material that is
characterized by a first refractive index for a first light signal;
and a first geometric anti-reflection (GAR) layer disposed on the
first surface, the GAR layer including a first plurality of
features that extend normally from the first surface, wherein each
feature of the first plurality thereof extends between a first base
located at the first surface and a first tip located at a first
boundary, and wherein each feature of the first plurality thereof
has a first cross-section that increases monotonically from the
first tip to the first base; wherein the first boundary is
characterized by a first effective refractive index that is lower
than the first refractive index.
Yet another embodiment in accordance with the present disclosure is
a method for forming an optical element, the method comprising:
providing a first substrate having a first surface, the first
surface comprising a first material having a first refractive index
for a first light signal; and forming a first geometric
anti-reflection (GAR) layer on the first surface, wherein the first
GAR layer includes a first plurality of features that extend
normally from the first surface from a first base located at the
first surface to a first tip at a first boundary, and wherein each
feature of the first plurality thereof has a first cross-section
that increases monotonically from the first tip to the first base,
and further wherein the first boundary is characterized by a first
effective refractive index that is lower than the first refractive
index.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A depicts a schematic drawing of the transmission
characteristics of a light signal incident on a flat interface
between air and a silicon layer.
FIG. 1B depicts a schematic drawing of the transmission
characteristics of a light signal incident on a non-flat interface
between air and silicon where the interface comprises a geometric
anti-reflection layer in accordance with the present
disclosure.
FIG. 1C depicts a schematic drawing of a cross-sectional view of an
exemplary feature 110 in accordance with the present
disclosure.
FIGS. 2A-D depict schematic drawings of cross-sectional views of
several non-limiting examples of feature shapes in accordance with
the present disclosure.
FIGS. 3A-B depict schematic drawings of simplified perspective and
sectional views, respectively, of an illustrative embodiment of a
cuvette in accordance with the present disclosure.
FIG. 4 depicts operations of a method suitable for forming a
cuvette in accordance with the illustrative embodiment.
FIGS. 5A-C depict cross-sectional views of substrates 312-1 and
312-2 at different points in the formation of cuvette 300.
FIGS. 6A-B depict a comparison of the transmission of an input
signal through a prior-art cuvette and a cuvette in accordance with
the present disclosure, respectively.
FIGS. 7A-B depict schematic drawings of cross-sectional views of a
plano-convex lens and a prism, respectively, that include geometric
anti-reflection layers in accordance with the present
disclosure.
DETAILED DESCRIPTION
Embodiments in accordance with the present disclosure exploit the
fact that geometric features formed at a surface can increase the
absorption of radiation incident on that surface. As a result, less
radiation is reflected at the interface between the surface and
another medium due to a difference in their refractive indices.
Operating Principle
FIG. 1A depicts a schematic drawing of the transmission
characteristics of a light signal incident on a flat interface
between air and a silicon layer.
Layer 100A is a layer of single-crystal silicon having surface 102.
Layer 100A is bounded by air, which has a refractive index, n1, of
approximately 1.0, while the silicon of layer 100A has a refractive
index, n2, of approximately 3.5.
When light signal 104 is incident upon the flat air/silicon
interface defined by surface 102, a portion of its optical energy
reflects and a portion of its optical energy passes into layer
100A, as dictated by the reflectivity of the interface.
As would be apparent to one skilled in the art, the reflectivity
coefficient, r, for the light signal at the interface between the
two materials is given by the formula:
.times..times..times..times..times..times..times..times.
##EQU00001## and the reflectivity and transmissivity at surface 102
is given as r.sup.2 and 1-r.sup.2, respectively.
For a flat air/silicon interface, formula (1) shows that its
reflectivity is approximately 31%; therefore, approximately 31% of
the optical energy of light signal 104 reflects at surface 102 and
only approximately 69% of the light signal passes through the flat
air/silicon interface into layer 100A.
FIG. 1B depicts a schematic drawing of the transmission
characteristics of a light signal incident on a non-flat interface
between air and silicon where the interface comprises a geometric
anti-reflection layer in accordance with the present
disclosure.
Layer 100B includes layer 100A, as well as a geometric
anti-reflection (GAR) layer 108 disposed on surface 102.
GAR layer 108 includes a plurality of features 110, which extend
from plane P1 at surface 102 to plane P2 at boundary 112.
Features 110 are arranged in a two-dimensional arrangement on
surface 102 with an inter-feature spacing, s1, that is smaller than
the shortest wavelength included in light signal 104.
Features 110 are configured to realize a layer having a refractive
index that slowly increases in substantially adiabatic fashion from
a relatively lower effective refractive index, n.sub.e, at boundary
112 to the refractive index of the material of surface 102. As a
result, GAR layer 108 functions as a graded-index layer that serves
to mitigate reflection of light signal 104 at the air/silicon
interface.
FIG. 1C depicts a schematic drawing of a cross-sectional view of an
exemplary feature 110 in accordance with the present
disclosure.
In the depicted example, feature 110 is a silicon projection having
height h1 and extending from base 114 at surface 106 to tip 116,
thereby defining sidewall 118. It should be noted that the tips of
features 110 collectively define boundary 112.
In the depicted example, sidewall 118 has a curved shape that gives
rise to a cross-section for the feature that increases
monotonically from a diameter of d1 at tip 116 to a diameter of d2
at base 114; however, as discussed below, feature 110 can have any
of myriad shapes that mitigate reflection of light signal 104
without departing from the scope of the present disclosure.
Furthermore, although features 110 and surface 102 comprise the
same material in the depicted example, in some embodiments,
features 110 are made of a different material than that at surface
102.
In the depicted example, geometric anti-reflection layers AR1 and
AR2 are configured to provide broadband anti-reflection
functionality that extends across the spectral range from
approximately 2 microns to approximately 15 microns. Exemplary
dimensions for feature 110, therefore, include h1 is approximately
5 microns, d1 is approximately 460 nm, d2 is approximately 1.8
microns, and s1 is approximately 2.0 microns. It should be noted
that a wide range of dimensions and spacing of features 110 can be
used to provide anti-reflection functionality for a light signal
having a given spectral range without departing from the scope of
the present disclosure.
Furthermore, as will be apparent to one skilled in the art after
reading this Specification, suitable ranges of dimensions and
spacings for the features of a geometric anti-reflection layer are
dictated by the spectral range of the light signal for which it is
intended to provide anti-reflection functionality.
It should be noted that geometric anti-reflection functionality can
be achieved with a wide range of shapes for features 110.
FIGS. 2A-D depict schematic drawings of cross-sectional views of
several non-limiting examples of feature shapes in accordance with
the present disclosure.
Feature 110A is analogous to feature 110; however, feature 110A has
a concave sidewall.
Feature 110B is analogous to feature 110; however, feature 110B has
a substantially linear sidewall such that feature 110B is has a
cone shape.
Feature 110C is analogous to feature 110B; however, feature 110C
includes nanostructure 120, which serves to increase the surface
area of sidewall 118C and improves the ability for features 110C to
mitigate reflection of light signal 104. Nanostructure 120 can be
formed via any conventional nano-structuring process, including,
without limitation, electro-chemical etching, ion-assisted etching,
and the like. It should be noted that nanostructure 120 can be
included in any feature of a geometric anti-reflection layer
without departing from the scope of the present disclosure.
Feature 110D is also analogous to feature 110; however, feature
110D is formed by etching into surface 102. It should be noted that
the inverted structure of feature 110D results in surface 102
defining boundary 112, while the plurality of tips 116D in GAR
layer 108 collectively define boundary 122. As a result, the
effective refractive index of a geometric anti-reflection layer
comprising features 110C adiabatically increases from n.sub.e to n2
along the z-direction from boundary 112 to boundary 122.
FIGS. 3A-B depict schematic drawings of simplified perspective and
sectional views, respectively, of an illustrative embodiment of a
cuvette in accordance with the present disclosure. Cuvette 300
includes body 302, chamber 304, optional channel 306, and optional
open port 308. The sectional view of cuvette 300 depicted in FIG.
3B is taken through line a-a as shown in FIG. 3A. For clarity,
geometric anti-reflection layers 108-1 through 108-4 are not shown
in FIG. 3A.
Cuvette 300 is a sample holder operative for enabling optical
interrogation of test sample 314 with interrogation signal 318. In
the depicted example, test sample 314 is blood and interrogation
signal 320 is a mid-infrared light signal having a spectral range
centered at 8.5 microns and that spans the spectral range from
approximately 2 microns to approximately 15 microns. It should be
noted, however, that cuvettes in accordance with the present
disclosure can be configured for use with a wide range of test
samples (preferably liquid or liquid-like) and/or interrogation
signals that span any suitable spectral range centered and/or have
any suitable center wavelength.
Test sample 314 is loaded into chamber 304 via channel 306 and
inlet port 310. In some embodiments, test sample 314 is loaded into
chamber 304 in another conventional manner. For example, test
sample 314 can be located in the chamber before substrates 312-1
and 312-2 are joined, etc.
Open port 308 is a channel that extends from chamber 304 to an edge
of cuvette 300. Among other functions, open port 308 enables air to
escape from chamber 304 as test sample 314 is loaded into it.
FIG. 4 depicts operations of a method suitable for forming a
cuvette in accordance with the illustrative embodiment. Method 400
is described with continuing reference to FIGS. 2-3A-B, as well as
reference to FIGS. 5A-C.
Method 400 begins with operation 401, wherein GAR layer 108-1 is
formed at surface 314-1 of substrate 312-1.
In the depicted example, each of substrates 312-1 and 312-2 is a
conventional single-crystal substrate. Prior to beginning method
400, substrate 312-1 has major surfaces 502 and 504 and substrate
312-2 has major surfaces 510 and 512.
In some embodiments, at least one of substrates 312-1 and 312-2 is
made of a material other than single-crystal silicon. Materials
suitable for use in one or both of substrates 312-1 and 312-2
include, without limitation, silicon, polysilicon, silicon
compounds (e.g., silicon carbide, silicon germanium, etc.),
compound semiconductors, glasses, silicon nitrides, silicon
oxynitrides, ceramics, composite materials, and the like.
FIGS. 5A-C depict cross-sectional views of substrates 312-1 and
312-2 at different points in the formation of cuvette 300.
In the depicted example, GAR layer 108-1 is formed by defining a
mask layer on major surface 502 of substrate 312-1. Once the mask
layer is formed, a non-directional reactive-ion etch (RIE) is used
to etch into substrate 312-1 at major surface 502 to define
features 110. It should be noted that the formation of features 110
also forms surface 316-1 from which the features extend.
Furthermore, since features 110 and surface 316-1 are formed by
etching into substrate 312-1, which is a homogeneous single-crystal
silicon substrate, features 110 and surface 316-1 also comprise
single-crystal silicon.
In the depicted example, tips 116 are portions of major surface 502
that remain after definition of the features. As a result, plane
P2-1 is co-located with the major surface of substrate 312-1. In
some embodiments, features 110 are formed such that major surface
502 is completely removed.
It should be noted that subtractive patterning via photolithography
and etching is merely one exemplary method for defining features
110 within the scope of the present disclosure. In some
embodiments, features 110 are grown on surface 316-1 via a
conventional deposition method, such as the Langmuir-Blodgett
method, self-assembly, atomic-layer deposition (ALD), evaporation,
sputtering, evaporative or sputtered deposition through a shadow
mask, selective-area growth, and the like. Furthermore, by growing
features 110, they can comprise a material that is different than
the surface from which they extend. In such embodiments, surface
316-1 is typically major surface 502.
At operation 402, cavity 506 is defined in substrate 312-1. In the
depicted example, cavity 506 is defined by forming a mask layer on
outer surface 504 and etching into substrate 312-1 via a
conventional etching technique, such as RIE, deep-RIE,
crystallographic-dependent etching, and the like. The definition of
cavity 506 defines intermediate surface 508.
FIG. 5A depicts a cross-sectional view of substrate 312-1 after the
formation of GAR layer 108-1 and cavity 506.
It should be noted that the order in which GAR layer 108-1 and
cavity 506 are formed can be reversed.
At operation 403, GAR layer 108-2 is formed at surface 314-2 of
substrate 312-1. GAR layer 108-2 is formed by defining features 110
and surface 316-2 by etching into substrate 312-1 at intermediate
surface 508, as described above and with respect to the formation
of GAR layer 108-1. It should be noted that, typically, GAR layer
108-1 is protected with a layer of photoresist or other suitable
protective layer during operation 403.
FIG. 5B depicts a cross-sectional view of substrate 312-1 after the
formation of GAR layer 108-2 at surface 314-2.
At operation 404, GAR layer 108-3 is formed at surface 316-3 of
substrate 312-2. GAR layer 108-3 is formed by defining features 110
and surface 316-3 by etching into substrate 312-2 at major surface
510, as described above and with respect to the formation of GAR
layer 108-1.
At operation 405, GAR layer 108-4 is formed at surface 316-4 of
substrate 312-2. GAR layer 108-4 is formed by defining features 110
and surface 316-4 by etching into substrate 312-2 at major surface
512, as described above.
FIG. 5C depicts a cross-sectional view of substrate 312-2 after the
formation of GAR layers 108-3 and 108-4.
At operation 406, substrates 312-1 and 312-2 are joined by bonding
major surface 504 and surface 314-3. In the depicted example, the
surfaces are joined via oxygen-plasma-assisted bonding; however,
myriad alternative bonding methods, such as fusion bonding,
thermo-anodic bonding, gluing, soldering, and the like, can be used
without departing from the scope of the present disclosure.
FIGS. 6A-B depict a comparison of the transmission of an input
signal through a prior-art cuvette and a cuvette in accordance with
the present disclosure, respectively.
Cuvette 600 is a prior-art cuvette comprising body 602 and chamber
604.
Cuvette 600 is structurally analogous to cuvette 300; however,
cuvette 600 does not include GAR layers at surfaces 610-1 through
610-4, each of which is a flat surface of body 602 through which
input signal 606 passes. It should be noted that, for the sake of
comparison, no test sample is included in either of chambers 604
and 304.
As discussed above and with respect to FIG. 1A, each of surfaces
610-1 through 610-4 defines a flat air/silicon interface having a
reflectivity of approximately 31%. As a result, due to reflections
at each of surfaces 610-1 and 610-2, only approximately 48% of the
optical energy of input signal 606 reaches chamber 604. In similar
fashion, as the input signal passes through the remainder of body
602, additional reflections at surfaces 610-3 and 610-4 further
reduce the optical energy in the light such that output signal 608
contains only 23% of the optical energy of input signal 606.
In contrast, each of surfaces 316-1 through 316-4 includes a GAR
layer 108 such that the combination of each GAR layer and its
respective surface is collectively characterized by a reflectivity
of only approximately 1%. As a result, approximately 98% of the
optical energy of input signal 606 reaches chamber 304 of cuvette
300 through surfaces 316-1 and 316-2 and their respective GAR
layers 108-1 and 108-2, and only another approximately 2% is lost
passing back out of body 302 through surfaces 316-3 and 316-4 and
their respective GAR layers 108-3 and 108-4. As a result, output
signal 608 contains approximately 96% of the optical energy of
input signal 606.
It is clear, therefore, that the addition of geometric
anti-reflection layers at each surface of a cuvette through which
an interrogation signal passes can realize a greater than 4.times.
improvement in the strength of the output signal.
It should be noted that, while the illustrative embodiment is a
low-reflectivity cuvette for holding a test sample, the concepts of
the present disclosure can be used to reduce the reflectivity of a
surface of a wide range of optical elements other than a sample
cuvette, such as optical elements (e.g., lenses, prisms, etc.). The
inclusion of a geometric anti-reflection layer on a preferably
high-transmissive surface is particularly advantageous for optical
elements made of high-refractive-index materials, such as silicon,
etc.
FIGS. 7A-B depict schematic drawings of cross-sectional views of a
plano-convex lens and a prism, respectively, having geometric
anti-reflection layers in accordance with the present
disclosure.
Lens 700 includes lens body 702, GAR layer 108-5, and GAR layer
708.
Lens body 702 has the shape of a conventional plano-convex and
includes convex surface 704 and planar surface 706. Lens body 702
is made of single-crystal silicon; however, other materials can be
used for lens body 702 without departing from the scope of the
present disclosure.
GAR layer 108-5 is disposed on planar surface 704 to realize a
low-reflectivity, planar air/silicon interface as described above
and with respect to FIG. 18.
GAR layer 708 is analogous to GAR layer 108-5; however, GAR layer
708 is disposed on a curved surface to realize a low-reflectivity,
curved air/silicon interface.
In similar fashion, prism 710 includes prism body 712 and GAR
layers 108-6 and 108-7.
Prism body 712 is characterized by a conventional prism shape and
is made of single-crystal silicon.
GAR layers 108-6 and 108-7 are disposed on surfaces 714 and 716,
respectively, to realize low-reflectivity, planar air/silicon
interfaces as described above and with respect to FIG. 1B.
It should be noted that lens 700 and prism 710 are merely examples
of low-reflectivity transmissive optical elements that can include
one or more GAR layers and myriad alternative optical elements are
within the scope of the present disclosure.
It is to be understood that the disclosure teaches just one example
of the illustrative embodiment and that many variations of the
invention can easily be devised by those skilled in the art after
reading this disclosure and that the scope of the present invention
is to be determined by the following claims.
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